This invention relates generally to nuclear reactors and, more particularly, to apparatus for repairing jet pump riser assemblies within a nuclear reactor pressure vessel.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core plate and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide.
Water enters the RPV through an inlet nozzle in the RPV sidewall. As is well known, a jet pump riser assembly is coupled to the inlet nozzle and the jet pump riser assembly typically includes, in part, a thermal sleeve, a lower elbow and a riser pipe. The thermal sleeve extends through the inlet nozzle and is welded to one end of the elbow. The other end of the elbow is welded to the riser pipe. The riser pipe is positioned between and extends substantially parallel to the RPV sidewall and the shroud.
During operation, the jet pump assembly directs recirculation flow within the RPV. Accordingly, substantial amounts of water are forced through the jet pump assembly and significant hydraulic forces are exerted on the jet pump assembly, including on the jet pump assembly elbow. Furthermore, and during operation, a large amount of heat is generated within the RPV, thus placing thermal stress on the jet pump assembly. These hydraulic forces and thermal stresses can increase the susceptibility of metal in the jet pump riser assembly to Intergranular Stress Corrosion Cracking (IGSCC), and in extreme cases the riser pipe could separate from the thermal sleeve which is undesirable.
It would be desirable to provide an apparatus which provides support for a jet pump riser assembly. It also would be desirable to provide such an apparatus which is easy to install.